The metal binding properties of chicken ovotransferrin and human serum transferrin will be characterized. Initial studies are done on chicken ovotransferrin because of its relative inexpensiveness. The protein side chains of human serum transferrin involved in iron binding will be characterized by using chemical modification as a major tool. Also, anion binding sites in the protein will be studied by similar procedures. With the anion binding site, the main approach will be an attempt at affinity labeling by using anions with potentially reactive groups capable of forming derivatives of protein side chains in the vicinity of the anion binding site. The chemical modifications will be divided into two types: those directed at changing the function activites of particular residues (active center residues) and those directed at changing physical properties of the molecule. The chemical modifications directed at particular residues will include those directed at arginines, histidines, and tyrosines. The chemical modifications directed at changing physical properties will include attachment of sugars, hydrophobic residues (e.g., benzyl) and amino acids. These studies will then be extended to study the transfer of iron from iron serum transferrin into the developing reticulocyte.